Chair

ABSTRACT

A chair has a seat  1  and a backrest  2  and the backrest  2  is allowed to be tilted backward by elastic deformation of right and left back frame devices  4 . The right and left back frame devices  4  each are composed of two unit frames  43  and  44 . The back frame device  4  has a main portion  4   a  which are disposed outside the right and left sides of the seat  1 , upper inward portions  43   a  and  44   a  which are connected to an upper rear end of the main portion  4   a , lower inward portions  43   b  and  44   b  which go under the seat  1  from a lower end portion of the main portion  4   a , and forward end portions  43   c  and  44   c  which are integrally connected to the lower inward portions  43   b  and  44   b . The forward end portions  43   c  and  44   c  are fixed to the base  7 . The back frame device  4  can be largely elastically deformed with the combination of a characteristic in which the back frame device is long, a characteristic in which the back frame device has the lower inward portions  43   b  and  44   b , and a characteristic in which the back frame device has the forward end portions  43   c  and  44   c . Accordingly, the backrest  2  can be tilted backward at a large angle.

TECHNICAL FIELD

The present invention relates to a chair with a backrest supported by aframe.

BACKGROUND ART

As a chair having a relatively simple structure, there is a chair inwhich a backrest is attached to a frame device including bars or pipes.The chair of this type is allowed to have a rocking function so that thebackrest is tilted backward by the leaning of a person sitting on aseat. An example thereof is described in Patent Document 1.

That is, in Patent Document 1, a frame device of a chair includes rightand left lower horizontal portions which elongates in back and forthdirections and placed on a floor, right and left front legs which risetoward the upper side from front ends of the lower horizontal portions,upper horizontal portions which extend to the rear side from upper endsof the right and left front legs, and right and left rear legs whichrise from rear ends of the lower horizontal portions, and a seat isattached to the right and left upper horizontal portions.

Rear ends of the right and left upper horizontal portions rise towardthe upper side and the right and left upper horizontal portions areintegrally connected to each other at a horizontally long lower portion.The horizontally long portion is connected to a lower back face of abackrest. Further, the upper ends of the right and left rear legs areconnected to each other by a horizontally long upper portion and thehorizontally long upper portion is connected to a back face of amid-height portion of the backrest. The backward tilting of the backrestof the chair in Patent Documents 1 is realized because the rear legsresist elasticity and are thus tilted backward, mainly.

Meanwhile, Patent Document 2 describes an example of a rotating chairwhich has a leg column formed of a gas cylinder and in which a seat anda backrest are supported by a frame device. Further, in a chairdisclosed in Patent Document 3, a frame device has a shape opened towardthe rear side in a side view and is fixed to a base, and a backrest isattached to a rear portion of the frame device.

Patent Document 1: Japanese Patent Publication No. 8-15446

Patent Document 2: Japanese Translation of PCT Application No. 9-502631

Patent Document 3: Japanese Registered Design Publication No. 390617

DISCLOSURE OF THE INVENTION Problem that the Invention is to Solve

In order to improve comfort in a rocking state, it is effective that abackrest is tilted backward as much as possible. Accordingly, in thecase of a chair in which a backrest is rocked using elastic deformationof a frame, it is required to largely deform the frame as much aspossible. However, in the case of the chair in Patent document 1, sinceonly the rear legs of the frame are elastically deformed, a backwardtilting amount of the backrest is small and a problem occurs in thatthere is a limit on improvement of comfort in a rocking state.

In addition, it can be said that, in the chair in Patent Document 2, arocking function using bending of the frame device is rarely expectedbecause the seat and the backrest only slide in back and forthdirections as a whole. Further, it is not known whether the chair inPatent Document 3 has a rocking function.

The present invention is contrived in view of the problems and a mainobject of the invention is to provide a chair which can ensure animproved rocking function together with a simple structure.

A chair of the present invention has a seat which is supported by abase, a backrest which is tiltable backward, and back frame deviceswhich have main portions positioned outside the right and left sides ofthe seat and support the backward tilting of the backrest. The backwardtilting of the backrest is allowed by elastic deformation of the backframe devices.

As a character of the present invention, the main portions of the rightand left back frame devices have a shape opened toward the rear side ina side view. In addition, as another character of the present invention,an upper connecting portion to which the backrest is attached isprovided at an upper rear end of the main portion of the back framedevice, a lower connecting portion going under the seat is formedintegrally with a lower rear end of the main portion of the back framedevice, the lower connecting portion has an end portion extending to thefront side, and the end portion of the lower connecting portion is fixedto the base or the seat.

In the present invention, the main portion of the back frame device canbe replaced with the word “side frame” to adopt a representation methodthat the side frame is provided with an upper connecting portion and alower connecting portion.

In the present invention, the whole back frame device can be elasticallytilted. Further, since the main portion of the back frame device has ashape opened toward the rear side in a side view, a total length of theback frame device is long. A deformation amount of the back frame devicecan be increased because of the shape of the main portion. This is afirst functional characteristic of the present invention.

In addition, a screwing action and a bending action are applied to thelower connecting portion forming a lower portion of the back framedevice upon rocking and thus the lower connecting portion is easilyelastically deformed. This is a second functional characteristic of thepresent invention.

In the present invention, the back frame device can be largelyelastically deformed with the combination of the characteristics. As aresult, it is possible to ensure an improved rocking function togetherwith a simple structure.

The “base” in the present invention represents a member supporting theseat and thus a leg is also in a category of the base. When the legincludes a gas cylinder, it is thought that the base is fixed to anupper end of the gas cylinder and the leg and the base are differentmembers. However, when the leg is formed of a pipe or a plate, the seatand the back frame device can be attached to the leg, and thus in thiscase, the leg and the base are identifiable.

The present invention has various variations and these will be describedas follows.

(1). Variation in Relationship between Backrest and Seat

The present invention includes two configurations. One is that the seatand the backrest are integrally connected to each other, and the otheris that the seat and the backrest are not connected. When the seat andthe backrest are connected to each other, the backrest is supported bythe seat and thus a burden on the back frame device is reduced.Accordingly, it can be said that the present invention is particularlyvaluable in a chair of a type in which the seat and the backrest areintegrally connected to each other.

Regardless of the connection between the seat and the backrest, there isa high tendency to improve a fitting property to a body when the seat istilted backward upon rocking. Moreover, the present invention alsoincludes a configuration in which the seat and the backrest are tiltedbackward together in a state of being connected to each other. Thebackrest and the seat are integrally tilted backward in thisconfiguration and thus a comfortable rocking state can be provided to auser. It is preferable that a degree of the backward tilting of the seatis smaller than a degree of the backward tilting of the backrest.

In one configuration of the present invention, a rising portionsupporting a waist of a person sitting on the seat is formed at a rearend of the seat and the backrest is connected to the rising portion tobe tiltable backward. Under this configuration, the waist of the personis supported by the rising portion of the seat even in a rocking stateand thus a so-called lumbar support function can be ensured.

(2). Variation in Structure of Back Frame Device

The structure of the backrest attachment to the back frame device canemploy various modes. For example, a bracket may be provided at rightand left ends of the backrest to be connected to the upper rear end ofthe main portion of the back frame device by pins.

In one configuration of the present invention, upper inward portionswhich extend along a back face of the backrest are formed to be bent atthe upper rear ends of the main portions of the right and left backframe devices, respectively, and the upper inward portions serve as theupper connecting portion. This invention has an advantage in that thestructure is simple and the backrest can be strongly supported.

The right and left back frame devices each can be formed of one member.However, in a preferable mode of the present invention, the right andleft back frame devices each includes a plurality of unit framesextending substantially parallel to each other. The back frame device ofthe present invention is bent complicatedly as a whole. Accordingly,when the right and left back frame devices each includes a plurality ofunit frames, a phenomenon in which the unit frames are deformedrestrictively each other occurs and thus it is possible to preventexcessive deformation even when employing thin members (bar-shapedmembers or pipes). This is an advantage of the present invention.

When the right and left back frame devices each includes a plurality ofunit frames, it is preferable that each back frame device is composed oftwo unit frames in view of appearance and economy. Further, it ispreferable to employ metal bars or pipes as a material for the unitframe, and particularly, it is preferable to employ steel or stainlessround bars in view of strength.

In the present invention, an armrest can be attached to an upper portionof the main portion of the back frame device. That is, the back framedevice also serves as an armrest support member and this is economical.In one configuration of the present invention, under the assumption thatthe right and left back frame devices each includes two unit frames, thetwo unit frames extend substantially parallel to each other in the mainportion in a top view and in a front view, and the armrest is attachedto an upper portion of the main portion. Thanks to this configuration,the armrest can be stably attached.

Further, in another configuration of the present invention, in theattachment of the armrest to the two unit frames of the back framedevice, the two unit frames are disposed at different heights so thatthe unit frame close to the seat is lower than the unit frame distantfrom the seat. Thus, an upper face of the armrest has a postureobliquely tilted downward toward the seat in a front view. The upperface of the armrest can have a horizontal posture. However, when theupper face of the armrest is tilted downward toward the seat while aperson sitting on the seat outstretches his right and left arms (thatis, the arms are tilted outside in a front view) and puts each elbow onthe armrest, the elbow is put on the upper face of the armrest at nearly90 degrees and thus stability of the elbows becomes good. This is alsoan advantage of the present invention.

Furthermore, in another configuration of the present invention, the mainportion of the back frame device has a substantially horizontallydirected V-shape, in a side view, in which a backward tilting portionand a forward tilting portion are continuously connected to each other.In this configuration, excessive deformation of the main portion issuppressed and thus a proper elastic characteristic can be ensured. Inaddition, since a space opened toward the front side in a side view isgenerated between the main portion of the back frame device and theseat, there is an advantage in that, for example, the back frame devicedoes not interfere with even a person who sits on the seat and stretchesout his legs. Moreover, the main portion of the back frame device is amost appealing portion. When the main portion is formed in a horizontalV-shape, it gives a sharp impression to people and thus it can be saidthat this is excellent in view of design.

(3). Variation in Cross-Section Structures of Backrest and Seat

In the present invention, the backrest and the seat include both of asingle layer structure and a multilayer structure. In one configurationof the present invention, the backrest has a back inner shell of which afront face is covered with a cushion and a back outer shell which isdisposed on the back side of the back inner shell, and the upper inwardportion of the back frame device is disposed between the back innershell and the back outer shell. The chair of the invention has a goodappearance because the upper inward portion of the back frame device isnot exposed.

Further, in another configuration of the present invention, the backouter shell of the backrest is formed of a wooden plate, and in the backouter shell, a backward protruding portion for avoiding the interferencewith the upper inward portion of the back frame device is formed to bebent and extends over the entire horizontal length. The seat has a seatouter shell which is formed of a wooden plate and a seat inner shellwhich is disposed on an upper face thereof and covered with a cushion,and the seat outer shell and the back outer shell have substantially thesame thickness and extend to be continuous each other in a side view.

The reason why the back outer shell and the seat outer shell are formedof a wooden plate is mainly requirement in design and cost. Using woodwhich is a recyclable resource is helpful in view of global environment.Since the outer shell of the backrest is provided with the backwardprotruding portion, the outer shell and the inner shell of the backrestare brought in contact with each other as closely as possible and theinterference of the back frame device with the outer shell is avoided.Thus, an excellent appearance is obtained.

The present invention will be better understood through the followingspecific examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a chair of a first embodiment as viewedfrom the front and FIG. 1B is a perspective view of the chair as viewedfrom the back;

FIG. 2A is a top view of the chair, FIG. 2B is a front view of thechair, and FIG. 2C is a right side view of the chair;

FIG. 3 is a top view illustrating the framework of the chair;

FIG. 4 is a sectional view of a base;

FIG. 5A is a longitudinal sectional side view and FIG. 5B is a sectionalview taken along the line B-B of the longitudinal sectional side view inFIG. 5A;

FIG. 6A is a sectional view taken along the line VIA-VIA in FIG. 5A andFIG. 6B is a sectional view taken along the line VIB-VIB in FIG. 5(A);

FIG. 7A is a sectional view taken along the line VIIA-VIIA in FIG. 2B,FIG. 7B is a side view of a cap, FIG. 7C is a view taken along the lineC-C in FIG. 7B, and FIG. 7D is a sectional view taken along the lineVIIB-VIIB in FIG. 2B;

FIG. 8 is a top sectional view taken along the line VIII-VIII in FIG. 4;

FIG. 9 is a sectional view taken along the line IX-IX in FIG. 8;

FIG. 10A is a top view of a holding member for a lifting and droppingoperation lever and FIG. 10B is a sectional view taken along the lineB-B in FIG. 10A;

FIG. 11 is a sectional view taken along the line XI-XI in FIG. 4;

FIG. 12A is a sectional view taken along the line XII-XII in FIG. 3 andFIG. 12B is a perspective view of a cover;

FIG. 13 is a perspective view of a chair of a second embodiment;

FIG. 14 is a perspective view of a chair of a third embodiment;

FIG. 15 is a front view of the chair;

FIG. 16 is a top view illustrating the framework of the chair;

FIG. 17 is a view illustrating the movement of the chair;

FIG. 18 is a side view of a chair of a fourth embodiment; and

FIG. 19A is a front view of the fourth embodiment and FIG. 19B is a topview taken along the line XIXB-XIXB in FIG. 18.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   -   1: SEAT    -   2: BACKREST    -   3: LEG    -   4: BACK FRAME DEVICE    -   4 a: MAIN PORTION OF BACK FRAME DEVICE    -   7: BASE    -   8: SEAT OUTER SHELL    -   9: SEAT INNER SHELL    -   10: SEAT CUSHION    -   11: BACK OUTER SHELL    -   12: BACK INNER SHELL    -   13: BACK CUSHION    -   17: HINGE    -   43: FIRST UNIT FRAME    -   44: SECOND UNIT FRAME    -   43 a, 44 a: UPPER INWARD PORTION AS ONE EXAMPLE OF UPPER        CONNECTING PORTION    -   43 b, 44 b: LOWER INWARD PORTION CONSTITUTING LOWER CONNECTING        PORTION    -   43 c, 44 c: FORWARD END PORTION CONSTITUTING LOWER CONNECTING        PORTION

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

A first embodiment is applied to a so-called rotating chair. The chairhas a seat 1 and a backrest 2 which are integrally connected to eachother, a leg 3 which supports the seat and the backrest, and right andleft back frame devices 4 for holding the backrest 2 to be rocked. Theleg 3 has a plurality of branch feet 3 a radially extending in a topview and a leg column 5 formed of a gas cylinder, and a caster 6 isprovided at a front end of the branch foot 3 a. A base 7 having acircular shape when viewed in a downward direction is fixed to an upperend of the leg column 5. The shape of the base 7 is not limited to thecircular shape and any shape can be selected.

For example, as illustrated in FIG. 5A, the seat 1 has a seat outershell 8 made of plywood (wooden board), a resin seat inner shell 9overlapping with an upper face of the seat outer shell 8 and fixedthereto, and a seat cushion 10 covering an upper face of the seat innershell 9.

The backrest 2 has a back outer shell 11 made of plywood (wooden board),a back inner shell 12 disposed in front of the back outer shell, and aback cushion 13 covering a front face of the back inner shell 12.Needless to say, the cushions 10 and 13 are covered with cloth (outercover material). Any of resin and metal can be employed as a materialfor the back inner shell 12. In the case where it is required to ensurestrength, it is preferable to employ metal (for example, sheet metal oraluminum die-casting product).

The seat inner shell 9 and the back inner shell 12 are provided withribs 14 and 15 overlapping with the outer shells 8 and 11, respectively.The seat outer shell 8 and the back outer shell 11; and the seat innershell 9 and the back inner shell 12 are manufactured as differentmembers, respectively. As illustrated in FIGS. 2A, 2B and 7D, areinforcing plate 16 made of a thin metal plate is fixed to a rear lowerface of the seat outer shell 8 and the reinforcing plate 16 and the backinner shell 12 are connected by a hinge 17 to be rotatable relative toeach other. A front end portion of the reinforcing plate 16 is fixed tothe seat outer shell 8 by a presser plate 18 made of a metal plate.

The seat outer shell 8 and the back inner shell 12 may be directlyconnected by the hinge 17 without the use of the reinforcing plate 16.In addition, the seat inner shell 9 and the back inner shell 12 may beconnected by the hinge and the seat inner shell 9 and the back outershell 11 may be also connected by the hinge. Moreover, the seat innershell 9 and the back inner shell 12 may be also manufactured to beintegral with each other (in this case, it is preferable to form aflexible hinge portion).

The seat inner shell 9 and the seat outer shell 8; and the back innershell 12 and the back outer shell 11 are held to be integral with eachother, respectively, by a pair of male and female snap members fitted toeach other by deformation occurring against elasticity. Needless to say,they may be fixed to each other by a fastening tool such as a machinescrew.

A rear portion of the seat inner shell 9 and a rear portion of the seatouter shell 8 slightly rise while gently curved in a side view (in FIG.5A, reference sign 1 a is the rising portion of the seat 1).Accordingly, it can be said that a lower portion of the backrest 2 isconfigured by the seat inner shell 9 and the seat outer shell 8 or theseat 1 is provided integrally with a pelvis supporting portion. However,in this description, the seat 1 includes the rising portions of the rearportion of the seat outer shell 8 and the seat inner shell 9 (this isfor convenience in description).

In general, the seat 1, the backrest 2 and the connecting portion (thatis, support shaft of hinge 17) are disposed at a height near a lowerportion of a lumbar area of a person sitting on the seat.

(1)-2. Specifications of Base and Attachment Structure of Seat

As illustrated in FIGS. 4, 5A, 8 and 9, the base 7 has a cylindricalbody 21, and an upper plate 22, an intermediate plate 23 and a lowerplate 24 are disposed in the cylindrical body 21. The plates 22, 23 and24 are fixed to the cylindrical body 21 by welding and a bush 25 isfixed to central portions of the plates 22, 23 and 24 by welding. Anupper end portion of the leg column 5 is fitted to the bush 25.

For example, as illustrated in FIGS. 3 and 4, a pair of right and leftstopper rods 26, which are vertically long and each of which ispartially fitted into the base 7, are disposed under the seat outershell 8. A horizontal support plate 28 is fixed to the upper end of thestopper rod 26 by welding and the support plate 28 is fixed to the seatouter shell 8 by a machine screw.

For example, as illustrated in FIGS. 4, 8 and 11, a seat support 27surrounding the bush 25 from the right, left and rear sides is fixed tothe lower plate 24 of the base 7 by welding (In FIG. 4, an upper face ofthe seat support 27 overlaps with the intermediate plate 23, butactually, as illustrated in FIG. 9, a gap exists between the seatsupport 27 and the intermediate plate 23).

The seat support 27 is provided with column portions 27 a which have aforwardly tilted posture in a side view and rise while extendinghorizontally in a front view, and the front end of the support portion27 a is formed integrally with a horizontal portion 27 b which facesright and left directions. The horizontal portion 27 b of the seatsupport 27 is pressed and held in the seat outer shell 8 by holdingpieces 29. The holding piece 29 is covered with a cover 30.

The cover 30 has a cantilever beam-shaped overhanging portion 30 afitted between the seat outer shell 8 and the horizontal portion 27 band a rib 30 b overlapping with a lower face of the holding piece 29. Asshown by the arrow A in FIG. 3, the cover is attached to the horizontalportion 27 b by being inserted thereto from the outside and thus afastening tool such as a machine screw is not required.

In addition, the overhanging portion 30 a of the cover 30 is firmlyinserted between the horizontal portion 27 b of the seat support 27 andthe seat ouster shell 8, and a lower face of the horizontal portion 27 aof the seat support 27 is brought into contact with a bottom face of theholding piece 29. Accordingly, the seat support 27 is held in the seatouter shell 8 without rattling.

An auxiliary stay 31, which is curved in a forward convex shape in a topview, is fixed to the base of the right and left horizontal portions 27b of the seat support 27 by welding. Accordingly, the seat 1 issupported only by the auxiliary stay 31.

The lower end of the rod 26 is a free end. In a non-sitting state, thelower end of the stopper rod 26 is positioned near an upper face of theintermediate plate 23 of the base 7. In addition, the seat 1 resistselastic deformation of the seat support 27 and can be thus tiltedbackward. When the seat 1 is tilted backward, the stopper rod 26 isdropped, and a maximum backward tilting angle of the seat 1 isrestricted by the reach of the stopper rod 26 to the lower plate 24 ofthe base 7. The upper plate 22 of the base 7 has a long hole 22 a (seeFIG. 4) for allowing the stopper rod 26 to be rotated. The intermediateplate 23 of the base 7 is notched so as not to interfere with thestopper rod 26.

A lever 33 for lifting and dropping the seat 1 is disposed under a frontportion of the seat 1. The lever 33 is manufactured by bending one bar(or pipe) and has a shape curved in a forward concave shape (or archedshape) in a top view as a whole. Accordingly, the lever 33 employs aform pulled upward under right and left corner portions of the seat 1.The main reason for employing such a form is that, when lower legs of aperson enter under the seat 1, it is avoided that the lower legs reachto the operation lever 33.

(1)-3. Attachment Structure of Lifting and Dropping Operation Lever

Next, an attachment structure of the operation lever 33 will bedescribed based on FIGS. 8 to 10. The base of the operation lever 33 hasa shape almost the same as a U-shape in a top view and has right andleft front-rear long portions 33 a which extend parallel to each otherwith a gap interposed therebetween and horizontally long horizontalportions 33 b which are formed so as to be opposed to the right and leftfront-rear long portions 33 a, respectively. An operation piece 35 forpushing a push rod 34 of the operating piece leg column 5 is fixed tothe right and left horizontally long horizontal portions 33 b bywelding, and the right and left horizontally long horizontal portions 33b other than the operation piece 35 are pressed and held in the upperface of the intermediate plate 23 of the base 7 by holding members 36,respectively.

In the holding member 36, right and left middle portions are notched soas not to interfere with the operation piece 35 and a portion pressingthe horizontally long horizontal portion 33 b is bifurcated. A rear endportion of the holding member 36 is provided with a hook 38 which isfitted to a long hole 37 formed on the intermediate plate 23 of the base7 and hung so as not to move upward. By putting the hook 38 on the edgeof the long hole 37 from the lower side, the rear end portion is fixedby one machine screw 39 so as not to be shifted. The holding member 36is interposed between the front-rear long portions 33 a of the operationlever 33 from the right and left sides and thus the operation lever 33is not horizontally shifted.

When a finger is caught on right and left end portions of the operationlever 33 to pull the portions upward, the operation lever 33 is rotatedaround the horizontally long horizontal portion 33 b, and thus a bushvalve 34 of the leg column 5 is pushed down by the operation piece 35and the lock of the leg column (gas cylinder) 5 is released. In anon-operation state, the front-rear long portion 33 a of the operationlever 33 overlaps with the upper face of the intermediate plate 23 ofthe base 7. Accordingly, the operation lever 33 is held so as not tofall down in the non-operation state.

(1)-4. Frame Device for Back

Next, the back frame devices 4 will be described. The back frame devices4 have main portions 4 a which are positioned outside the right and leftsides of the seat 1. The main portion 4 a has a backward tilting portion4 b constituting an upper portion with respect to a front end thereof asa boundary and a forward tilting portion 4 c constituting a lowerportion with respect to the front end thereof as a boundary. The wholemain portion has a V-shape opened toward the rear side.

A continuous portion (that is, front end portion of main portion 4 a) ofthe forward tilting portion 4 c and the backward tilting portion 4 b ofthe main portion 4 a is curved in an arc shape in a side view. Further,a degree of the tilting of the backward tilting portion 4 b is smallerthan a degree of the tilting of the forward tilting portion 4 c. Thereason of this is that an armrest 42 is attached to the backward tiltingportion 4 b. In addition, the backward tilting portion 4 b and theforward tilting portion 4 c are gently curved in a side view so as toform a concave shape toward an opposite direction.

The right and left back frame devices 4 each are composed of unit frames43 and 44 formed of two round bars, and both of the whole unit frames 43and 44 extend substantially parallel to each other. In the followingdescription, when it is required to distinguish the two unit frames 43and 44 from each other, the unit frame close to the seat 1 is referredto as the first unit frame 43 and the unit frame distant from the seat 1is referred to as the second unit frame 44 with reference to thepostures in the main portion 4 a for convenience. A bar made of metalsuch as steel, stainless or aluminum can be used as a material for bothof the unit frames 43 and 44.

The first unit frame 43 and the second unit frame 44 have upper inwardportions 43 a and 44 a bent and going behind a back face of the backinner shell 12 from the rear end of the main portion 4 a, respectively.In this case, the upper inward portion 44 a of the second unit frame 44is positioned higher than the upper inward portion 43 a of the firstunit frame 43, and the upper inward portions 44 a of the right and leftsecond unit frames 44 each are pressed and held in the back inner shell12 by presser portions (bearing members) 45. The presser portion 45 isfixed to the back inner shell 12 by a machine screw. The upper inwardportion 44 a of the second unit frame 44 can be slightly rotatedrelative to the presser member 45 and the back inner shell 12.

In this embodiment, the upper inward portions 44 a of the right and leftsecond unit frames 44 are continuously connected to each other. Thus,the right and left second unit frames 44 are manufactured using oneround bar as a material. In this embodiment, since the right and leftupper inward portions 44 a extend in series, there is an advantage inthat the tilting of the backrest 2 becomes smooth.

The upper inward portion 43 a of the first unit frame 43 has a setlength so as to abut on or be brought into close contact with thepresser member 45. Since the upper inward portion 43 a is set to havesuch a length, right-left positioning of the back frame device 4 and thebackrest 2 is automatically performed.

It is preferable that the upper inward portion 43 a of the first unitframe 43 and the upper inward portion 44 a of the second unit frame 44are integrally connected to each other by welding or the like. The backouter shell 11 overlaps with the back face of the back inner shell 12.Accordingly, in order to prevent the upper inward portions 43 a and 44 aof the unit frames 43 and 44 to interfere with the presser member 45, abackward protruding portion 11 a curved in a mountain shape is formed tobe bent in the back outer shell 11. A tunnel-shaped space is generatedbetween the back outer shell 11 and the back inner shell 12 by formingthe backward protruding portion 11 a and this space can be sealed with acap 46 illustrated in FIGS. 7C and D.

For example, as illustrated in FIG. 3, the first unit frame 43 and thesecond unit frame 44 are provided with lower inward portions 43 b and 44b, which are horizontally long and go under the seat 1 while beingcontinuously connected to the rear end of the front tilting portion 4 cof the main portion 4 a, respectively. In back of the base 7, the lowerinward portions 43 b and 44 b go under the seat 1 and the front ends ofthe lower inward portions 43 b and 44 b are integrally connected toforward end portions 43 c and 44 c. The forward end portions 43 c and 44c are fixed to the intermediate plate 23 of the base 7 by welding. Inthis embodiment, the lower connecting portion described in the claimsincludes the lower inward portions 43 b and 44 b which are horizontallylong and the forward end portions 43 c and 44 c.

Needless to say, a cylindrical body 21 of the base 7 is notched so asnot to interfere with the forward end portions 43 c and 44 c. Asillustrated in FIG. 8, long holes 47 and notched portions 48 overlappingwith the forward end portions 43 c and 44 c in a top view are formed inthe intermediate plate 23 of the base 7 and this is a measure forfacilitating overlaying upon welding of the forward end portions 43 cand 44 c.

In this embodiment, the lower inward portion 43 b and the forward endportion 43 c of the first unit frame 43 are surrounded by the lowerinward portion 44 b and the forward end portion 44 c of the second unitframe 44 from the outside. This is because the forward end portions 43 cand 44 c are disposed at the same height. By changing the heights of theforward end portions 43 c and 44 c, the forward end portions 43 c and 44c can achieve a posture overlapping with each other in a top view andcan be fixed to a side face of the base 7.

The first unit frame 43 and the second unit frame 44 are set to be atdifferent heights so that the first unit frame 43 is lower than thesecond unit frame 44 at a position in the backward tilting portion 4 bof the main portion 4 a. In addition, as illustrated in FIG. 5B, a platemember 49 having a posture tilted in a front view is fixed to the firstunit frame 43 and the second unit frame 44 of the backward tiltingportion 4 b by welding and the armrest 42 is fixed to the plate member49.

Since the plate member 49 is tilted in a front view, an upper face ofthe armrest 42 is tilted downward toward the seat 1 in a front view.Accordingly, when a person sitting on the seat outstretches his arms andputs each elbow on the armrest 42, the arms are put from a directionsubstantially perpendicular to the upper face of the armrest 42 as shownby the arrow B in FIG. 5B and thus the elbows can be stably held. Thearmrest 42 is separated into two upper and lower members 42 a and 42 band the upper and lower members 42 a and 42 b are fastened by screws(not shown) passing through the plate member 49.

(1)-5. Conclusion

When a person sitting on the seat leans on the backrest 2, a largemoment is applied to an upper portion of the backrest 2 and thus thebackrest 2 is largely tilted backward around the hinge 17 by elasticdeformation of the back frame device 4.

Further, states, specifically, a state “a” in which since the back framedevice 4 has a long length and a substantially V-shape in a side view,the back frame device is easily deformed, a state “b” in which since thelower inward portions 43 b and 44 b are present under the back framedevice 4, an action (torsion action) is applied to the lower inwardportions 43 b and 44 b to screw them around axes thereof, and thus theback frame device 4 is largely and easily deformed in a direction sothat the backward tilting angle of the backrest 2 increases, and a state“c” in which the screwing action and the bending action are also appliedto the forward end portions 43 c and 44 c and thus they are allowed tobe deformed, are given, and the back frame device 4 is largelyelastically deformed with the combination of the states a to c. As aresult, the backrest 2 can be largely tilted backward.

The back frame device 4 is composed of two inner and outer unit frames43 and 44. Since both of the unit frames 43 and 44 have differentlengths and are disposed at different heights, the unit frames 43 and 44are deformed in different manners and deformation occurs with mutualrestriction. That is, a phenomenon in which one of the unit frames 43and 44 is deformed while the other acts as resistance occurs.

In this case, the sum of the elastic deformation of the two unit frames43 and 44 becomes resistance to the backward tilting of the backrest 2and the forward advance of the seat 1. The unit frames 43 and 44restrict each other as the degree of the deformation increases, and thusan increasing rate of the elastic restoring force of the unit frames 43and 44 as a whole is higher than an increasing rate of the backwardtilting angle of the backrest 2. As a result, the backrest 2 is notsteeply tilted backward. The backrest is tilted backward with anappropriate resistance force. In this manner, the chair of thisembodiment can provides a comfortable feeling upon rocking.

In this embodiment, the seat 1 is tilted backward and either one of thefollowing two modes, specifically, a mode in which the seat is initiallytilted backward since a person sitting on the seat leans on the backrest2 and a mode in which the seat is slightly tilted backward since aperson sits on the seat, can be selected as the backward tilting mode ofthe seat 1. The mode is determined depending on the setting of thestrength (elastic restoring force) of the seat support 27.

Second Embodiment

FIG. 13 illustrates a second embodiment. In this embodiment, a leg 3 hasa four leg-type frame structure. The portions disposed above the base 7are essentially the same as them of the first embodiment. However, thelifting and dropping operation lever 33 of the first embodiment is notprovided (in this second embodiment, the lifting and dropping operationlever is not required).

In the case where the leg 3 has a frame structure composed of pipes orbars, various types are conventionally proposed. The present inventioncan be applied to any conventional leg and can be also applied to newlymanufactured legs.

Third Embodiment

FIGS. 14 to 17 illustrate a third embodiment. This embodiment has thesame basic configuration as that of the first embodiment and there aredifferences in details. Hereinafter, a description will be given.Descriptions for the same parts as those of the first embodiment will beomitted if not particularly necessary.

In this embodiment, a seat 1 and a backrest 2 have a structure in whichsubstrates 1 a and 2 a such as synthetic resin or plywood are coveredwith cushion members 1 b and 2 b, respectively, and the substrate 1 aand 2 a of the seat 1 and the backrest 2 are integrally connected toeach other (the substrates 1 a and 2 a correspond to the outer shells 8and 11 of the first embodiment, respectively). The backrest 2 is bent ina side view around a bending point 17′ (fold) positioned at a heightnear a waist of a person sitting on the seat.

As a method of bending the backrest 2, as illustrated in FIG. 17, thesubstrate 2 a may be separated into upper and lower portions to connectboth of the portions to each other by a hinge 17 or a pin, or thesubstrate 2 a may be made of a flexible material such as resin to form athin hinge portion.

As illustrated in FIGS. 15 to 17, the seat 1 is attached to seat frames51 attached to a base 7. The seat frames 51 are formed in asubstantially crank shape with lower horizontal portions 51 a which arehorizontally long in a front view, vertically long portions 51 b whichare formed to be bent at opposite ends of the lower horizontal portions,and right and left upper horizontal portions 51 c which are formed atopposite ends of the vertically long portions. The lower horizontalportion 51 a is fixed to the base 7 or attached to be rotatable relativeto the base 7 via a lower bearing member 52. The upper horizontalportion 51 c of the seat frame 51 is attached to be rotatable relativeto a lower face of the seat 1 by an upper bearing member 53.Accordingly, when the seat frame 51 is rotated around the upperhorizontal portion 51 a, the seat 1 can slide forward and backward.

First and second unit frames 43 and 44 are provided with column portions4 d rising in a vertical direction in a front view on the right and leftsides of the seat 1, upper portions 4 e extending backward while beingcontinuously connected to the upper ends of the right and left columnportions 4 d, and lower portions 4 f which are horizontal in a side viewand extend backward while being continuously connected to the lower endsof the right and left column portions 4 d. By the column portion 4 d,the upper portion 4 e and the lower portion 4 f, a main portion 4 aopened toward the rear side is configured.

Lower inward portions 43 b and 44 b which are horizontally long extendcontinuously from the rear ends of the lower portions 4 f and forwardend portions 43 c and 44 c are formed integrally with the front ends ofthe lower inward portions 43 b and 44 b. The forward end portions 43 cand 44 c are fixed to the base 7 by welding.

Moreover, the rear end of an upper portion 4 e of the second unit frame44 is integrally connected to one upper inward portion 44 a extendingalong a back face of a portion near the upper end of the backrest 2 andthe upper inward portion 44 a is connected to the back face of thebackrest 2 by presser members 45 to be relatively rotated. The upperportion 4 e of the first unit frame 43 is fixed to the upper inwardportion 44 a of the second unit frame 44 by welding.

The upper inward portion disposed inside the backrest 2 may be made of adifferent member from that for both of the unit frames 43 and 44 and theupper portions 4 e of the unit frames 43 and 44 may be fixed to theupper inward portion by welding or the like. Furthermore, the first unitframe 43 may be provided with an upper inward portion 43 a which isformed to be bent.

As illustrated in FIGS. 15 and 16, the second unit frame 44 and thefirst unit frame 43 extend substantially parallel to each other in a topview and in a front view, except the upper inward portion 44 a.

In this embodiment, when the seat frame 51 is fixed to the base 7, theseat 2 only moves forward upon rocking. On the other hand, when the seatframe 51 is connected to the base 7 to be tiltable, the seat 1 movesforward upon rocking. In addition, the front end of the seat 1 may bedropped by forward movement (that is, forward tilting).

A function of the back frame device 4 is essentially the same as that ofthe first embodiment. However, it can be said that since a length of theback frame device 4 is longer than that of the first embodiment and thefirst unit frame 43 and the second unit frame 44 are not connected toeach other in the main portion 4 a, deformation occurs more easily inthis embodiment than in the first embodiment.

Fourth Embodiment

FIGS. 18 and 19 illustrate a fourth embodiment. In this embodiment, aback frame device is formed of one member. Since a shape of a back framedevice 4 is almost the same as in the third embodiment, the samereference signs as in the third embodiment are given and details will beomitted. An upper inward portion is represented by reference sign 4 g, alower inward portion is represented by reference sign 4 h, and a forwardend portion is represented by reference sign 4 i. In the relationshipwith the above-described embodiments, the reference sign 4 g correspondsto the reference signs 43 a and 44 a, the reference sign 4 h correspondsto the reference signs 43 b and 44 b, and the reference sign 4 icorresponds to the reference signs 43 c and 44 c.

In this embodiment, a pair of front and rear seat frames 51 is disposed.The seat frame 51 may be fixed to a base 7 and may be connected to thebase 7 to be tiltable. The forward end portion 4 i of the back framedevice 4 is fixed to a lower face of the base 7.

(5). Others

The present invention can be embodied in various forms other than theabove embodiments. For example, a forward end portion of a lowerconnecting portion of a back frame device is tiltable in a top view.That is, for example, tilting can be achieved so that right and leftspaces of right and left forward end portions become wider as beingclose to the rear side. In addition, the lower connecting portion may beformed in an arc shape in a top view.

Furthermore, when a main portion of a back frame device is formed in asubstantially V-shape in a side view, an upper face or a lower facethereof may be formed in a horizontal shape. The main portion of theback frame device may be also formed in a U-shape opened toward the rearside in a side view.

In this description, it is disclosed that the back frame device iscomposed of a plurality of the unit frames and the connecting portion ofthe back support frame is provided with the end portion extending insubstantially front and rear directions, and these can be embodied asindependent inventions.

1. A chair comprising: a base; a seat supported by the base; a backrestwhich is backwardly tiltable; and a back frame device including mainportions positioned outside right and left side of the seat, wherein thetilt of the backrest is supported by the back frame device and isallowed by elastic deformation of the back frame device; and the each ofmain portions has a shape opened toward rear end in a side view andcomprises: an upper connecting portion to which the backrest isattached, positioned at a upper rear end of each of the main portions;and a lower connecting portion which goes under the seat integrallyformed with a lower rear end of each of the main portions, wherein thelower connecting portion has an end portion extending to the front side;and the end portion is fixed to the base or the seat.
 2. The chairaccording to claim 1, wherein upper inward portions which extend along aback face of the backrest are formed to be bent at the upper rear endsof the main portions of the right and left back frame devices,respectively, and the upper inward portions serve as the upperconnecting portion.
 3. The chair according to claim 1, wherein a risingportion which can support a waist of a person sitting on the seat isformed at a rear end of the seat, and the backrest is connected to anupper end of the rising portion of the seat so as to be tiltablebackward.
 4. The chair according to claim 1, wherein the seat issupported by the base in a state of being tiltable backward, and theback frame device is fixed to the base.
 5. The chair according to claim1, wherein the right and left back frame devices each comprises aplurality of unit frames extending substantially parallel to each other.6. The chair according to claim 5, wherein the right and left back framedevices each comprises two unit frames formed of bars or pipes, the twounit frames extend substantially parallel to each other in the mainportion in a top view and in a front view, and an armrest is attached toan upper portion of the main portion.
 7. The chair according to claim 6,wherein the two unit frames are disposed at different heights so thatthe unit frame close to the seat is lower than the unit frame distantfrom the seat in the portion to which the armrest is attached, and thusan upper face of the armrest has a posture obliquely tilted downwardtoward the seat in a front view.
 8. The chair according to claim 1,wherein the main portion of the back frame device has a portion whichconstitutes an upper portion with respect to a front end thereof as aboundary and is tilted backward in a side view and a portion whichconstitutes a lower portion with respect to the front end thereof as aboundary and is tilted substantially forward in a side view, and theportion tilted backward and the portion tilted forward in a side vieware smoothly and continuously connected to each other via a front endportion having an arc shape in a side view, and thus the whole mainportion has a substantially horizontal V-shape.
 9. The chair accordingto claim 2, wherein the backrest has a back inner shell of which a frontface is covered with a cushion and a back outer shell which is disposedon the back side of the back inner shell, and the upper inward portionof the back frame device is disposed between the back inner shell andthe back outer shell.
 10. The chair according to claim 9, wherein theback outer shell of the backrest is formed of a wooden plate, and in theback outer shell, a backward protruding portion for avoiding theinterference with the upper inward portion of the back frame device isformed to be bent and extends over the entire horizontal length, andwherein the seat has a seat outer shell which is formed of a woodenplate and a seat inner shell which is disposed on an upper face of theseat outer shell and covered with a cushion, and the seat outer shelland the back outer shell have substantially the same thickness andextend to be continuously connected to each other in a side view. 11.The chair according to claim 1, further comprises a seat supportconnecting the seat and the base.
 12. The chair according to claim 11,wherein the seat support is connected to the seat at front side ascompare to the base.